Corrosion resistant articles having a zinc surface and process for preparing the same

ABSTRACT

ARTICLES HAVING A ZINC SURFACE SUBJECT TO WHITE RUSTING ARE COATED WITH LECITHIN TO IMPROVE THE CORROSION RESISTANCE. THE INVENTION ESPECIALLY USEFUL FOR RETARDING WHITE RUSTING OF GALVANIZED STEEL.

United States Patent CORROSION RESISTANT ARTICLES HAVING A ZINC SURFACE AND PROCESS FOR PREPAR- ING THE SAME James-G. Morrison, Coraopolis, Pa., assignor to National Steel Corporation No Drawing. Filed July 9, 1969, Ser. No. 840,517

Int. Cl. B44d 1/34; B05b 5/02; C09d 5/08 US. Cl. 117-17 25 Claims ABSTRACT OF THE DISCLOSURE Articles having a zinc surface subject to white rusting are coated with lecithin to improve the corrosion resistance. The invention is especially useful for retarding white rusting of galvanized steel.

BACKGROUND OF THE INVENTION This invention broadly relates to a novel process for' treating materials having a zinc surface to inhibit white rusting and to generally improve the corrosion resistance. The invention further provides zinc surfaced articles characterized by improved corrosion resistance.

The invention will be described and illustrated herein-. after with specific reference to a process for inhibiting white rusting of materials having a zinc surface. However, the process of the invention also may be used for retarding or inhibiting other types of corrosion and for generally improving the corrosion resistance of articles having a zinc surface. The term zinc surface as used in the specification and claims is intended to embrace materials having a surface area subject to white rusting which is composed of zinc or predominantly of zinc. Examples of materials having a zinc surface subject to white rusting and suitable for treatment in accordance with the present invention include metallic articles composed entirely of zinc or an alloy containing predominantly zinc, and basis metals such as ferrous metal provided with a protective coating of zinc or an alloy containing a predominant amount of zinc. Suitable materials for treatment may have a zinc surface as defined herein on only a portion of the surface area.

A fresh bright untreated zinc surface exposed to the atmosphere soon develops a film of corrosion products which are produced by the action of atmospheric substances such as oxygen, carbon dioxide and moisture. As the corrosion proceeds, the film of corrosion products tends to increase in thickness.

White rust is a term often used to refer to a specific form of the above mentioned type of corrosion, and it is usually considered to be a relatively thick white deposit of corrosion products composed largely of zinc hydroxide and basic zinc carbonate. White rust forms rapidly when water is confined against an unprotected zinc surface, and it is especially severe where fresh, bright untreated zinc surfaced sheets or shapes are arranged during storage or shipment so that water can accumulate between adjacent surfaces and remain for extended periods of time. The coating of white rust gradually thickens and eventually the pleasing appearance of the initially bright zinc surface is destroyed and it takes on the appearance of an inferior product.

The art has long sought an entirely satisfactory process for treating zinc surfaced materials to effectively inhibit white rust formation. In general, the prior art processes involve the application of either a relatively thick organic protective coating such as oils, waxes, greases, varnishes and paints, or various chemical treatments which deposit a thin inorganic protective coating integral with the zinc Patented June 13, 1972 surface. A number of the prior art processes are not entirely unsatisfactory due to their 'being ineffective for substantially completely eliminating white rust formation over a reasonable period of time, too expensive, or too time consuming. Additionally, the prior artchemical treatments often require careful control of operating conditions such as concentrations of ingredients and temperature of treatment and exhibit a pronounced tendency toward formation of a colored film on the treated zinc surface. The foregoing and still other disadvantages of the prior art processes are overcome by the present invention.

It is an object of the present invention to provide a novel process for treating materials having a zinc surface to improve the corrosion resistance.

It is a further object to provide a novel process for inhibiting white rusting of galvanized ferrous metal.

It is a still further object to provide zinc surfaced articles characterized by improved corrosion resistance.

It is still a further object to provide galvanized ferrous metal characterized by improved resistance to white rustmg.

Still other objects and advantages of the invention will be apparent from the following detailed description and the examples.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED VARIANTS THEREOF In accordance with the present invention, material having a zinc surface is treated to inhibit white rusting and to generally improve the corrosion resistance by applying a coating of lecithin thereon. As will be discussed in greater detail hereinafter, there are certain preferred procedures, treating conditions and materials which may be employed to produced superior results.

The zinc surfaced material to be coated with lecithin may be given a conventional wet pretreatment for the removal of oil, grease, dirt and other surface contaminants. The presence of a thin film of oxide on the zinc surface usually is not detrimental, but in instances where a large amount of corrosion has taken place it may be: necessary to remove the corrosion products prior to coating with lecithin. Freshly galvanized surfaces need not be treated to remove the thin oxide film prior to application of the lecithin coating.

The lecithin may be applied to the clean zinc surface by a number of coating processes. In one variant, the zinc surface is wetted with a volatilizable liquid containing lecithin, and thereafter the liquid is evaporated to deposit the lecithin coating. The volatilizable liquid may be an organic solvent for lecithin and in such instances an organic solution thereof is applied to the zinc surface. In other instances, the volatilizable liquid may be a nonsolvent for lecithin and the lecithin may be applied to the zinc surface in the form of a finely divided suspension.

Suitable organic solvents for lecithin include hydrocarbons, alcohols, ketones and esters which are liquid under the conditions of application. Examples of hydrocarbons include aliphatic hydrocarbons containing approximately 5-20 carbon atoms and preferably about 6-10 carbon atoms such as hexane, heptane, octane and nonane, and aromatic hydrocarbons containing about 6-25 and preferably about 6-12 carbon atoms such as benzene, toluene and xylene. Normally liquid distillate fractions derived from petroleum such as kerosene, light gas oil, light fuel oil and diesel fuel are very useful. Mixtures of the foregoing hydrocarbons may be used when desired. Examples of alcohols include primary, secondary and tertiary alcohols containing approximately 1-18 carbon atoms and for better results approximately 1-8 carbon atoms, of which methyl, ethyl, propyl and isopropyl alcohols usually give the bestre'su'lts'. The ket one solvents may contain approximately 3:12carbonatoms and preferably: about -3-8 -car- 1-4 carbon atoms and alcohols containing 1-8 and preferablyabout 1-4 carbon atoms are useful, such as themethyl, ethyl, propyl, isopropyl, butyl, and isobutyl esters of formioacid, acetic acid, .propionic acid andbutyric acid. In-; instances where,the lecithin is appliedin the form of a liquid suspension, nonsolvents'for lecithin may be used ,asthe wolatilizable liquid. Water is usually the preferrednon'solvent; Oftena dispersing agent or detergent is not necessary when-preparing lecithin suspensions due to its detergent properties. Lecithin suspensions may be prepared by adding lecithin to water or other nonsolvents under agitation conditions sufiiciently vigorous to assure that the lecithin is dispersed in the form of finely divided particles. If desired, the lecithin may be subdivided by grinding or other suitable method to reduce the particle size to very small dimensions prior to forming the suspension. v

The amount of lecithin present in the volatilizable liquid may vary over wide ranges. However, it is usually preferred to apply a solution or suspension containing approximately 5-15 by weight of lecithin, and preferably about 10% -by weight. The volatilizable liquid may contain less than 10% by weight of lecithin in instances where large amounts of liquid may be evaporated readily.

Larger amounts of lecithin than 15% by weight may be present in the volatilizable liquid in instances where only a small amount of liquid may be evaporated readily. In one variant, a semi-solid to solid coating composition containing lecithin and sufiicient volatilizable liquid to produce a semi-solid cream or wax-like solid may be applied to the zinc surface, and the liquid content of the coating may be evaporated when desired, but this is not always necessary.

In another variant, a coating of lecithin is applied in the absence of a volatilizable liquid. This may be accomplished by intimately contacting the zinc surface with dry lecithin under pressure such as by vigorously rubbingthe zinc surface with lecithin. The zinc surface may be heated to anelevated temperature when desired.

I The lecithin alsomay be applied by electrostatically depositing a spray or aerosol of finely divided particles of lecithin on the zinc surface. The electrostatic charges on i 1 thelecithin particles causes them to adhere initially to the zinc surface, and thereafter the polar portion of the lecithin molecule causes the particles to adhere permanently. Preferably, the zinc surface is Wetted with a film of a volatilizable liquid at the time of electrostatically deposity;

up to about 175 F. The zinc surface substrate may be at a temperature sufiiciently elevated to evaporate the volatrl zable liquid when a lecithin solution or suspensionis applied.

temperature usually varies from about room temperature I Theamount of lecithin to be appliedto the zinc surface may'vary overwide ranges. The lecithin should be present in an amount to form a thin film or coating on the zinc surface and the upper limit on the thickness is largely of a practical nature. Preferably, the lecithin coating should have a thickness between about 3X10 inch and 1X 10- inch', and often a lecithin coating having a thickness of about 1X10 inch gives the best results.

Lecithin 1s commerciallyavailable and may be derived from a number of SOIHCESrMOSt lecithin-is-preparedfrom soy beans or corn, and soy bean lecithin is usually preferred. It is not necessary to employ a substantially pure grade of lecithin, as corrosion resistance is markedly improved when using the lowergrades which have a substantial lecithin content." I Q f. ';1 The" zinc surfaced substrate coated with"thesolution or dispersion of lecithin is preferably passed through-an oven to evaporate the liquid contentof'the'coating composition. The oven .shouldbe maintained at a sufliciently elevated temperature to result in evaporation of the volatilizab'le liquid component. The preferred temperature varies with the nature of the volatilizable liquid, but it must not be above the decomposition temperature of lecithin and is sufficiently elevated to result in a relatively rapid volatilization rate. The oventemperature may be, fol-example, fromv 10 0' na tO'BbQlJlI 250 F. The, f

regoingjdetailed'description and"the following examples are fof'purposes of illustration only, and are not intended as being limiting to the spirit or scope of the appended claims.

EXAMPLE .I' i

Soy bean lecithin is dissolved in kerosene in an amount to provide a 10% by weight solution. The resulting homo- 'geneous' solution of lecithin is applied to .clean untreated surfaces of apIurality of freshly galvani'zedsteel sheets by spraying at'a'delivery rate of 0.5' milliliter'per square foot'per'side" to produce a 0.1 mil coating of lecithin after evaporating the kerosene solvent-The solvent is removed by heating the coated galvanized steel sheets inan oven to a metal temperature of F. until the kerosene evaporates. I The lecithin coated galvanized steel sheets thus prepared are tested for white rust inhibition by the conventional test procedure. Comparative data are provided bysubecting a portion of the uncoated'sheets of galvanized steel to the same test environment: The uncoated and lecithin coated galvanized steel sheets are inspected periodically over the test period for visible white rusting. The lecithin coated sheets 'do not have visiblewhite rusting when the uncoated sheets exhibit white rusting on 10% of the surface area. a

EXAMPLE II The general procedure of Example I is followed with the exception of substituting an aqueous suspension .of lecithin for the kerosene solution of lecithin, employed in Example I. The suspension is prepared by avigorously agitating lecithin inwater using a high speed mixer with rotating blades. The suspension contains 10%.by weight of finely divided lecithin.

The suspension is sprayed on .clean untreated freshly galvanized steel sheets as in Example I, and the. water content of the coating is evaporated by heating in a forced air oven at 175 9 F. The lecithin coated galvanized steel sheets thus produced and uncoated but otherwise-identical galvanized steel sheets are tested as inExample I. The lecithin coated galvanized steel sheets have no visible white rust when the untreated and uncoatedgalvanized steel sheets have white ruston over 10% of their surface area.

EXAMPLE in A uniform film of water is applied to a plurality of clean untreated freshly galvanized steel sheets, and then the wetted sheets are passed through an electrostaticdeposition zone where a particulate coating of finely divided lecithin iselectrostatically deposited thereon. The lecithin coating has'a thickness of approximately 1 mil, and the water content in the coatin'g'is evaporated by heating in a forced air 'oven at a temperature of 175 'F. i

The lecithin coated galvanized steel sheets are tested as in E xample I for white rust inhibition and comparative data are obtained by testing the untreated and 'uncoate'd galvanized steel sheets under identical conditions. The lecithin coated sheets are free of visible white rust when the untreated and uncoated sheets have at least 10% of their surface area covered with write rust.

EXAMPLE IV Suflicient kerosene is added to lecithin with agitation to form a semi-solid paste having a paint or cream-like consistency. The coating composition thus produced is brushed on a plurality of galvanized steel sheets in an amount to provide a coating thickness of approximately 1 mil after drying the kerosene from the applied coating.

The lecithin coated sheets are dried in an oven at 175 F. to evaporate the small amount of kerosene in the coating. The period of time required for drying is much shorter than in Example I due to the markedly lower kerosene content in the coating.

The lecithin coated sheets thus produced are tested for white rust inhibition as in Example I, and comparative data are obtained for untreated and uncoated galvanized steel sheets under identical conditions. The lecithin coated galvanized steel sheets are free of visible white rust when the untreated and coated sheets have over 10% of their surface area coated with white rust.

I claim:

1. A process for treating galvanized ferrous metal subject to White rusting consisting essentially of the step of intimately contacting the surface of freshly galvanized steel with a coating composition consisting essentially of lecithin to deposit a thin film of lecithin thereon and thereby improve the corrosion resistance.

2. The process of claim 1 wherein the coating of lecithin has a thickness between about 3x10" inch and about 1X linch.

3. The process of claim 1 wherein the coating of lecithin has a thickness of about 1X10- inch.

4. The process of claim 1 wherein the coating of lecithin is applied by wetting the freshly galvanized steel surface with a volatilizable liquid containing lecithin, and thereafter the liqud is evaporated from the said surface to deposit a coating of lecithin thereon.

5. The process of claim 4 wherein the liquid contains about 5-15 by weight of lecithin.

6. The process of claim 4 wherein the liquid contains about by weight of lecithin. I

7. The process of claim 4 wherein the lecithin is dissolved in an organic solvent.

8. The process of claim 4 wherein the lecithin is dissolved in an organic solvent selected from the group consisting of hydrocarbons, alcohols, ketones and esters.

9. The process of claim 4 wherein the lecithin is dissolved in a hydrocarbon solvent.

10. The process of claim 4 wherein the lecithin is dissolved in a hydrocarbon solvent comprising an aliphatic hydrocarbon.

11. The process of claim 4 wherein the lecithin is dissolved in a distillate fraction derived from petroleum.

12. The process of claim 4 wherein the lecithin is dissolved in kerosene.

13. The process of claim 4 wherein the volatilizable liquid is a nonsolvent for lecithin, and the lecithin is dispersed in the nonsolvent in the form of finely divided particles.

14. The process of claim 13 wherein the nonsolvent for lecithin is water.

15. The process of claim 1 wherein a semi-solid to solid coating composition comprising an admixture of lecithin and a volatilizable'liquid is applied to the freshly galvanized steel surface.

16. The process of claim 1 wherein a particulate coating of finely divided particles of lecithin is applied to the freshly galvanized steel surface by electrostatic deposition.

17. The process of claim 16 wherein the freshly galvanized steel surface is wetted with a film of a volatilizable liquid at the time of electrostatically depositing the lecithin coating.

18. The process of claim 1 wherein the freshly galvanized steel surface is intimately contacted with lecithin under pressure to deposit the lecithin coating.

19. The process of claim 18 wherein the freshly galvanized steel surface is rubbed with lecithin to deposit the lecithin coating.

20. An article having a zinc surface subject to white rusting, the zinc surface having a coating consisting essentially of lecithin thereon to improve the corrosion resistance.

21. The article of claim 20 wherein the coating of lecithin has a thickness between about 3 l0- inch and about 1 10 inch.

22. The article of claim 20 wherein the coating of lecithin has a thickness of about 1 10- inch.

23. The article of claim 20 wherein the zinc surface subject to white rusting is on galvanized ferrous metal.

24. The article of claim 23 wherein the coating of lecithin has a thickness between about 3 10- inch and about 1 10 inch.

25. The article of claim 23 wherein the coating consists of lecithin and has a thickness of about 1X 10- inch.

References Cited UNITED STATES PATENTS 2,368,607 l/l945 White 117-134 X 2,375,007 5/ 1945 Larsen et a1. 106l4 2,634,237 4/ 1953 Kopf et al 1O6---14 X 2,665,232 1/1954 Neish 106-14 2,796,363 6/ 1957 Lalone 117134 X 2,884,338 4/1959 Jenison 117-134 X 2,918,390 12/1959 Brown et al 1l7134 X 2,921,858 1/1960 Hall 106-14 2,997,398 8/1961 Kronstein 106-14 3,021,228 2/ 1962 Gibson et a1 117--134 X WILLIAM D. MARTIN, Primary Examiner S. L. CHILDS, Assistant Examiner U.S. Cl. X.R. 

